The continuing aim of this research program is to explore the relations between environmental variables and the effects of drugs on behavior. The primary method of research is to develop repeatedly reproducible stable behavioral performances in experimental subjects using the techniques of operant conditioning. Performances involving substantial physical exercise will be developed in Rhesus monkeys. Both static and dynamic exercise will be studied. The cardiovascular system will be monitored during the exercise. The effects of drugs on endurance and on the cardiovascular system during exercise will be studied.